_ $ CustomClass显示错误，如匿名闭包所定义，返回类型'Type'不是'CustomClass'。 `

Question

I have add a new class TopicNew and run flutter pub run build_runner build --delete-conflicting-outputs in to a sample code from flutter_livestream_provider for learning.

But I have no idea why my class shows error

import 'package:built_value/built_value.dart';

part 'topicNew.g.dart';

abstract class TopicNew implements Built<TopicNew, TopicNewBuilder> {
  int get id;
  String get name;
  TopicNew._();
  factory TopicNew([updates(TopicNewBuilder b)]) => _$TopicNew;  #<- show error here
}

Answer 1

This is a syntax error.

Instead of:

 => _$TopicNew;

do:

 = _$TopicNew;

---

Factory constructors can be declared as

factory Classname(int a) = OtherClass;

This syntax is a shorthand for

factory ClassName(int a) => OtherClass(a);